Riveting tools for placing blind rivets have a tubular jaw housing in which a mandrel jaw is slidably disposed. The mandrel jaws are slidable coaxially under spring influence to cause the jaw members to cooperate with inclined internal faces of the jaw housing. The jaws tend to move radially inwardly to grip a rivet mandrel therebetween and each of the jaw members has faces at its end which converge towards its radial inner or mandrel gripping face for cam-wise cooperation with complimentary faces in the jaw carrier and in the nose or tip of the tool to move the jaws apart radially to receive the stem of a mandrel between them when the jaw housing is fully advanced to the nose or the tip of the tool. Such rivet setting tools and mandrel jaws are disclosed in the U.S. Pat. No. to Elliott, 3,324,700.